The present invention relates to a method of removing a film containing an organic composition, particularly to a method of removing a photoresist film containing an organic polymer composition used in a photolithographic process for producing a semiconductor device and the like, and to an apparatus used in the method.
A photoresist material is generally used in a photolithographic process for forming a fine pattern and/or in a subsequent etching step for forming an electrode pattern in course of manufacturing a semiconductor device, such as an integrated circuit, a transistor, a liquid crystal device, a diode and the like.
For example, when a silicon oxide layer is formed in a desired pattern on a semiconductor substrate such as a silicon substrate (referred to as a silicon wafer), a silicon oxide layer is first deposited on the surface of the substrate and cleaned before a photoresist material suited for forming the desired pattern is applied to the silicon oxide layer to form a photoresist film. Then, a photo mask having a pattern corresponding to the desired pattern is placed on the photoresist film, exposed to light and then developed. Thereby, a photoresist film having the desired pattern, referred to a photoresist pattern, is obtained. In the subsequent etching step, the silicon oxide layer is removed according to the resulting photoresist pattern. Finally, after the removal of the remaining photoresist film and the cleaning of the surface of the substrate, the silicon oxide layer is remained on the substrate in the desired pattern.
In the etching step, an art-known method of removing a part of the photoresist film unnecessary for the formation of the desired pattern includes, for example, [1] a method using an oxygen gas plasma and [2] a method using various oxidizing agents.
In the method using an oxygen gas plasma [1], an oxygen is introduced in the photoresist film under vacuum and a high voltage to generate an oxygen gas plasma. Then, the photoresist film is decomposed and removed by reacting with the oxygen gas plasma. However, there had been some problems in this method [1], including the requirement of an expensive apparatus for generating the oxygen gas plasma, a potential of damaging the substrate containing an electrical element due to the presence of charge carriers in the plasma, and the like.
Alternatively, as an example of the method [2] using various oxidizing agents to decompose and remove the photoresist film, for example, a method using hot concentrated sulfuric acid or a mixture of hot concentrated sulfuric acid and hydrogen peroxide as the oxidizing agent is known.
When using hot concentrated sulfuric acid, however, there is a disadvantage, such as an extremely high risk of heating strong sulfuric acid up to 150xc2x0 C.
On the other hand, when using the mixture of hot concentrated sulfuric acid and hydrogen peroxide, a substance having an oxidizing and decomposing action is released according to the following scheme. In the scheme, on adding hydrogen peroxide to hot concentrated sulfuric acid heated to about 140xc2x0 C., peroxosulfuric acid (H2SO5; generally referred to as Caro""s acid) and an oxygen atom (O) are generated as follows:
H2SO4+H2O2⇄H2SO5+H2Oxe2x80x83xe2x80x83(1)
H2O2xe2x86x92O+H2Oxe2x80x83xe2x80x83(2)
The organic photoresist film may be oxidized by the strong acidity of both peroxosulfuric acid and oxygen atom to be converted to an inorganic substance. The inorganic substance is decomposed by reacting with hot concentrated sulfuric acid and then removed from the surface of the substrate.
However, as shown in the above schemes (1) and (2), this method [2] has a problem that, since a sulfuric medium is diluted with water produced upon every addition of hydrogen peroxide to hot concentrated sulfuric acid, the concentration of hot concentrated sulfuric acid after mixing is decreased with time. The method [2] also has disadvantages, including the extremely high risk as described for the method [1], i.e. the use of strong sulfuric acid at an elevated temperature, and the heat generated when mixing hot concentrated sulfuric acid with hydrogen peroxide, and the necessity system generating strong ventilation in order to operate the method in a clean room, and the like.
As another oxidizing agent used to decompose the photoresist film other than hot concentrated sulfuric acid, there has been developed a water-immiscible solution for exclusively removing a photoresist film, such as, for example, a solution #106 consisting of 30% by volume of dimethylsulfoxide and 70% by volume of monoethanolamine. However, such oxidizing agent has problems, including its lower oxidation power than hot concentrated sulfuric acid and a mixture of hot concentrated sulfuric acid and hydrogen peroxide, and the difficulty of treating the foul solution which is immiscible with water.
In order to overcome the problems of the above methods [1] and [2], a method of removing a photoresist film using a mixture of ozone with hot sulfuric acid as the oxidizing agent has been proposed (Japanese Patent Kokai Publication No. Sho 57 (1982)-180132). This publication discloses decomposing and removing the organic substance (i.e. the photoresist film) or the inorganic substance deposited on the substrate or the insulating layer by bubbling an ozonized gas in hot sulfuric acid. It also describes a washing apparatus used in the method cross sectional view of the apparatus is illustrated in FIG. 8).
The washing apparatus shown in FIG. 8 includes a quartz container 6xe2x80x3 filled with hot concentrated sulfuric acid 5xe2x80x2 heated at approximately 110xc2x0 C., which is laid on a heater 11, and a quartz tube 120 having plural of outlet 3xe2x80x2. A raw gas (generally, oxygen) supplied through a gas-introducing tube 111 provided outside the quartz container 6xe2x80x3 is converted to an ozonized gas in on an ozone generator 1. The ozonized gas is then injected through the quartz tube 120 into hot concentrated sulfuric acid 5xe2x80x2 in the quartz container 6 to react with sulfuric acid, and thereby, peroxosulfric acid and an oxygen atom are produced. Oxidizing the photoresist film with the strong acidity of both peroxosulfric acid and oxygen causes the removal of the photoresist film from the surface of the substrate 8 (held with a substrate cassette 9) immersed in hot concentrated sulfuric acid.
In the method described in the above publication, the concentration of the sulfuric acid does not change since water is not generated during the decomposition of the photoresist film, and therefore, the frequency of changing the sulfuric acid may be decreased. The method, however, had a problem that the cost for raw materials is too high because a large amount of the sulfuric acid is needed to operate. Additionally, the method and apparatus disclosed in the above publication also have a high risk on working because of the use of strong sulfuric acid at an increased temperature in the same way as the conventional method, and also needs an extremely strong ventilation since the oxidizing agent is volatilized by bubbling the ozonized gas.
Accordingly, an object of the present invention is to provide a method of removing a photoresist film at an increased rate, which decreases both usage of the raw materials and the cost for any exhaust system and is also environment-friendly, and to further provide an apparatus used in the method, in order to overcome the above problems with the art-known method of removing the photoresist film and with the conventional apparatus used therefore.
As using herein, an xe2x80x9cozonized gasxe2x80x9d means a gas mixture containing oxygen and a given amount of ozone. Hereinafter, a xe2x80x9csealed systemxe2x80x9d is thermodynamically classified into an open system, but it means one in which any of a gas and a solution are introduced therein and a gas or a vapour generated in removing a photoresist film according to the present invention, and the like, are not to be released or spattered outside of the system forms.
According to the first aspect of the present invention there is provided a method of removing a photoresist film by in a sealed system, evenly and continuously or intermittently supplying a photoresist film-removable mixture containing an ozonized gas and a photoresist film-remover to a photoresist film formed on a surface of a substrate through a photoresist film-remover supplier arranged as opposed to the photoresist film. The ozonized gas used in the present invention contains in an amount of at least 5 mole %, preferably 5 to 100 mole % of ozone based on the total amount of the ozonized gas.
In the method of the present invention, a distance between a surface of the photoresist film on the substrate and the photoresist film-remover supplier may be within a range of 1 to 5 mm. By adjusting the distance to the above range, a rate of removing the photoresist film in the method according to the present invention may be further increased.
In the method of the present invention, the ozonized gas and the photoresist film-remover may be supplied separately or in a mixed form. The ozonized gas may be supplied under a high pressure of a range between 1 atm (101, 325 Pa) and 5 atms (506, 625 Pa).
A suitable photoresist film-remover used in the present invention may be selected from organic solvents having a lower reactivity with ozone, including saturated alcohols, ketons and carboxylic acids.
In the method of the present invention, both a temperature of the photoresist film-remover and a temperature at a region apart at least 5 mm from the surface of the substrate are preferably set at a lower temperature than the surface of the substrate.
In the present invention, most preferably, the ozonized gas may be continuously supplied, and the photoresist film-remover may be intermittently supplied.
Further, the method of the present invention may comprise a means of generating an electric field between the photoresist film-remover supplier and the surface of the substrate. By the means, the photoresist film-remover may be converted to a microparticle.
The second aspect of the present invention relates to an apparatus comprising a reacting chamber equipped with an ozonizer and an exhaust system, a stage for fixing the substrate having the photoresist film on the surface thereof, and a photoresist film-remover supplier arranged as opposed to the stage, wherein the stage and the photoresist film-remover supplier are distributed in the reacting chamber. An ozonized gas and a photoresist film-remover which are used as the photoresist film-removable mixture may be continuously or intermittently supplied to the surface of the substrate through the same or different apertures formed in the photoresist film-remover supplier.
In the apparatus of the present invention, the reacting chamber may be made of stainless steel or Teflon(copyright)-coated stainless steel, Teflon(copyright) resin, ceramics or Teflon(copyright)-coated ceramics, or a mixture thereof.
The ozonized gas used in the apparatus contains at least 5 mole %, preferably 5 to 100 mole % of ozone based on the total amount of the ozonized gas.
The ozonized gas and the photoresist film-remover may be preliminarily mixed to supply as the photoresist film-removable mixture. In this case, the ozonized gas and the photoresist film-remover are preferably preliminarily mixed to send the mixture thereof to the photoresist film-remover supplier and then supplied through the apertures.
In the apparatus of the present invention, a distance between a surface of the photoresist film on the substrate and the photoresist film-remover supplier may be within a range of 1 to 5 mm. The apparatus may also comprise a means of heating the stage and/or a means of cooling the photoresist film-remover. By using them, both a temperature of the photoresist film-remover and a temperature at a region apart at least 5 mm from the surface of the substrate may be set at a temperature lower than the surface of the substrate.
The apparatus may further comprise a means of heating the stage and/or a means of cooling the photoresist film-remover.
In the present invention, the ozonized gas may be supplied to the apparatus under a high pressure of a range between 1 atm (101, 325 Pa) and 5 atms (506, 625 Pa).
A suitable photoresist film-remover used in the apparatus of the present invention may be selected from organic solvents having a lower reactivity with ozone, including saturated alcohols, ketons and carboxylic acids.
The apparatus of the present invention may also comprise a means of generating an electric field between the photoresist film-remover supplier and the substrate.